Advanced microscopic imaging tools, such as a scanning electron microscope (SEM), are often used in inspection of semiconductor wafers in order to detect and classify defects in production of microelectronic devices. SEM images, however, contain a wealth of detail, which must be properly interpreted in order to identify the structures appearing in each image and to distinguish the defects from other features. Identification and delineation of the structures in such an image is commonly referred to as image segmentation. Various techniques are known in the art for automated segmentation of SEM images to assist in proper image interpretation.
In some cases, SEM images are segmented by comparing the images with computer aided design (CAD) data that have been used in production of the devices under inspection. For example, U.S. Pat. No. 7,792,351 describes a method for defect review using image segmentation, in which an electron image of the area containing a previously-detected potential defect is obtained. The image may then be aligned to the CAD layout of the integrated circuit. The alignment may be performed, for example, by locating a dominant edge in the image that is expected to be within the field of view (FOV) based upon the design information. Similarly, U.S. Pat. No. 8,036,445 describes a method of position matching between an image of a semiconductor pattern, such as a SEM image, and CAD data.
As another example of the use of CAD data in SEM image processing, U.S. Patent Application Publication US 2009/0238443 describes a method in which a correlation operation is used for determining positions of a critical dimension SEM (CD-SEM) image and a CAD data pattern (referred to as a template). Specifically, through an evaluation based on correlation operation for determining positions of the template and the CD-SEM image in two-dimensional directions, an X-Y position in which the template image and the CD-SEM image have the highest correlation is determined, and the template image is overlaid with the CD-SEM image at the position.
Other methods that use CAD data to assist in SEM image processing are described in U.S. Patent Application Publications US 2007/0092129, US 2009/0039263, US 2009/0266985, and US 2009/0236523.